Primer coating compositions



June 27, 1961 L. E. LONG 2,990,294

PRIMER COATING COMPOSITIONS Filed Feb. 25, 1957 United States Patent O 2,990,294 PRIMER COATING COR/[POSITIONS Lamar E. Long, Doylestown, Pa., assignor, by mesne asslgnments, yto Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Feb. 25, 1957, Ser. No. 641,839 19 Claims. (Cl. 117-75) This invention relates to a primer coating composition comprising a mixture of a halogen-containing polymer and a metal oxide frit. In one aspect this invention relates to a primer coating composition comprising a mixture of a polymer of a halogen-containing olefin and a metal oxide frit. In another aspect this invention relates to peruorohaloolen polymer composition which has improved adhesive characteristics. In another aspect the invention relates to chemically resistant coatings. Another aspect of the invention relates to chemically resistant laminates. Still another aspect of this invention relates to a method of preparing halogenated thermoplastic compositions having good adhesive characteristics and chemical resistance.

There is a widespread demand in industry for protective coatings which will withstand the effects of severe environmental conditions. Many protective coatings are currently available but these are useful only where high temperature and highly corrosive materials are not encountered.

Recent industrial developments have made available at high molecular Weight, uorinated olefin polymers. These fluorinated olefin polymers, for example, polymers of chlorotriuoroethylene, have a unique combination of physical and chemical characteristics which has led to their use in a variety of applications. Physically, these polymers which are flexible at low temperatures and extremely tough possess high thermal stability and excellent electrical properties and are, therefore, widely used as electrical insulation particularly in situations where high temperatures are expected. Chemically, these polymers offer excellent resistance to highly corrosive chemicals, such as fuming nitric acid, solvents such as anline, acetone, alkalies, such as sodium hydroxide, etc., and are therefore widely used where corrosive environment conditions are anticipated. Although the highly fluorinated olefin polymers as a group possess desirable physical and chemical characteristics, such as, in addition to those mentioned above, low permeability, zero moisture absorption, high abrasive resistance, high tensile strength, high impact strength, etc., their adhesive characteristics are poor, particularly their adhesion to metal surfaces. Therefore, it has been necessary to utilize various techniques in order to provide adhesion. For example, by one method, itis necessary to provide an adhesive coating to the surface and a mixed coating containing a major amount of the adhesive and a minor amount of the highly fluorinated polymer before the final coating of highly uorinated polymer can be applied. Other methods include sand blasting or etching the surface, however, these techniques provide only a mechanical bonding of the polymer to the surface of the substrate, and as a result, the polymeric coating does not have a lasting adherence.

It is, therefore, an object of this invention to provide a primer coating composition which combines good physical and chemical characteristics with lasting adhesive properties.

ICC

It is another object of this invention to provide an additive which, when mixed with a halogenated-containing polymer, provides an adherent coating on the surface of a substrate.

It is another object of this invention to provide a primer coating composition to which a final coating of halogenated polymer can be applied directly.

It is another object of this invention to provide an article of manufacture coated with a chemically resistant, thermally stable composition.

Another object of this invention is to provide peruorohaloolein polymer-glass cloth laminate lfor use under severe environmental conditions of temperature and corrosion.

Another object of this invention is to provide a strongly adherent perfluorohaloolen polymeric coating composition for metal surfaces.

Another object of this invention is to provide a commercially feasible method for preparing a primer coating composition.

Still another object of this invention is to provide a method for applying a chemically resistant coating oomposition to the surface of a substrate.

Various other objects and advantages of the present invention will become apparent to those skilled in the art from the accompanying description and disclosure.

According to this invention a primer coating composition containing a dispersion vehicle, halogen-containing polymer such as a peruorohalooleiin polymer, and a metal oxide frit of a metal above group IV of the periodic table having a melting point between about 600 C. and about l500 C. such as, for example, cobaltous oxide frit; is applied to a substrate such as, for example, a metal substrate, and is fused and cured thereon at a temperature of between about 350 F. and about 600 F.

The halogen-containing polymers in the primer coating composition of the present invention are plastic or elastomeric olelinic polymers, the monomers of which contain between 2 and 5 carbon atoms and at least one normally gaseous halogen atom (chlorine or fluorine) for every two carbon atoms in the olen monomer. The preferred polymers of the present invention are the polymers of perfluorohaloolens containing between 2 and 3 carbon atoms in the olefin monomer.

Examples of the preferred periluorohalooleiin polymers are the homopolymers of chlorotriuoroethylene, bromotriuoroethylene and tetrafluoroethylene; the copolymers of any combination of the above periluorohalogenated olen monomers and the copolymers of any of the above pertluorohalogenated olefin monomers as Well as perliuoropropene with hydrogen-containing halogenated olelins such as vinylidene uoride, vinyl fluoride, vinylidene chloride, vinyl chloride, trifluoroethylene, chlorofluoroethylene and 1,1,3-trifluorobutadiene.

Most preferred of the above-mentioned polymers are the polymers of chlorotriuoroethylene, namely, the homopolymer of chlorotriuoroethylene and the copolymer of chlorotrifluoroethylene and vinylidene uoride, which copolymer contains not more than 20 mole percent of vinylidene fluoride. v

Other halogenated olefin polymers which are usefully employed in the present invention are the homopolymers of vinylidene fluoride, vinylidene chloride, vinyl uoride, vinyl chloride, triuoroethylene, chlorouoroethylene and any polymeric combination of the above-mentioned monomers.

3. High molecular weight plastics or elastomers of the above-mentioned polymers having molecular weights above 50,000 are those which are preferably employed in this invention as distinct from low molecular weight polymers of the same monomers which exist in oil, grease and wax range. In applications of putties and caulking fluids, these lower molecular weight polymers may be employed. The high molecular weight polymers referred to are normall'y'solid and.havesofteliiiigpointsabovefl5()o C. and, in .the` case of hmopolyr'ners. of. chlorotriuoroethylene, have no. strength temperatures (NST.) of at least220 C. and preferably above 250 C. These high molecular weight. polymers kare. employed in the coating composittionsfand laminatesof the presentinvemion.

For the purpose of .this invention the preferred copolymer.ifz'chlorotriuoroethylene and vinylidene fluoride vcontains above about 80 moleY percent and below `100 mole percent chlorotritluoroethylene. Copolyrriers c on- -tainingbetween 70 andSO, mole percent of chlorotriuoroethylene have resinouscharacteristics and are soluble` inra number, of commonorganic solvents. Copolymers between 20 and 69 mole percent of chlorotriu'oro- Vethylene elastomeric. The selection of the proper copolymer mole ratio depends on the ultimate use and desired properties of the blend. However, it has beenV found. that for most coating compositions a chlorotriilioroethylene and. vinylideneuoride copolymer composition containing above 80 mole percent chlorotrifluoroethylene sdesirable. i

VIn theprocess, of. this invention a dispersion of polymer particles is preferably` employed wherein the. particle size1of the polymer is generally that of a finely divided powder, that iis, at least 95percent through a number l2 sieve, preferably a number 20K()` sieve in the U.S.-Burea u oi'gStandards Series. In theV case of a chlorotrifluoroethylene polymer the particle size is `most preferably not morethan 50 microns. f The .primer coating compositions of this invention are applied by techniques which require the presence of a volatile dispersing vehicle which preferably wets the particle surfaces of the halogen-containing polymer and in which the rpolymer and metal oxide frit is insoluble. However, it is also within the scope of this invention, particularly where themore soluble 'elastomeric polymers are employed, to prepare a solution of the polymer wherein. [the metal oxide fritparticles are suspended. Examples of volatile dispersing vehicles which may be suitably used in this invention are the aromatic hydrocarbons such as, for example, benzene, toluene, `xylene, etc.; aromatic and aliphaticl ketones such as, for example, methyl ethyl ketone, diisobutyl ketone, diphenyl ketone, etc., aliphatic esters such asamyl acetate, ethyl acetate, ethyl propionate, and water used in combination with any. soluble wetting agent such as, for example, acetone, butanol, pentanol, etc, Y

The metal oxide frit or primer which is blended with thc-.halogen-containiug polymerof this invention is the frit of a metal oxide selectedV from the group consisting of oxides of antimony, oxides of manganese, oxides of nickel and oxides ofcobalt. The metals of these oxides are'those metals which have melting points between 600 C. and about 1500* C. and are located in the fth, seventhandeeighth groups of the periodic table. This particular group vof metals, above group IV of the periodic table, having a. melting point between about 600"..C. andabout l500 C., are selected becanse the oxides ofV these metals are formed at high temperatures and `are capable of fusing with the -frrit at convenient temperatures and vwill not decompose or degrade-at the temperature of fusion. In thisinvention a'metal oxide constitiitesl'between aboutZ weight percent and about 85 Weishtgpsrcant. preferably between @91H50 weight per.: oeuf 1ancl'about 80 weight percent of the metal' c'pideI V it compound. The metal oxide frit is usually pepared'by 1 fusion of themetal oxide and the frit at a temperature above about 1000 C. Some metal oxide frits, for example, cobaltous oxide frit is commercially available and is supplied under that name by Harshaw Chemical Co., The Ferro Corp., and General Metallic Oxide Co., to name a few. For the purposes of this invention a frit is dened as the calcined or partially fused, but yet unvitri- Ktied, materials of which glass is made. An example of a typical frit is a complex alkaline borosilicate glass produced by melting a mixturelsuch as borax, feldspar, quartz and cryolite. The frit can be obtained from a number of manufacturers, namely, The O. Hommell Co.,A Harshaw Chemical Co., J. Pemio Corp. and others.

Of the primers which are suitablyblended with the halogen-containing polymer, frits of-cobalt oxides, namely cobaltous oxide (COO), cobaltic oxide (C0203), cobalto-,cobaltie oxide (C0304), are most preferred. Examptlesrof other metal;v oxide frits suitably blended with the gha'olgen-containing polymers ofV this invention are the frits of manganic oxide (MnzOB), manganous oxide (MnO), permanganate, (MngO-f), manganite or manganate (MnOz), niekelous oxide (N10), nickelic oxide (Ni'zosL'nickelous-nickelic oxide (Ni304), nickel per- Oxides (NiOg and Ni04), antimony trioxide (SbgOa), antmony tetroxide (SbZOg), and antimony pentoxide `(Sb205). In addition, any combination of theY aforementioned metal oxide frits can be used. In certain instances, where Aitis desirable to fuseV the halogen-containingfpolymer` at a higher temperature than is generally used, i.e. at a temperature of about 600 F. or higher, a chromium oxide, a molybdenum oxide and/or a molybvdenrnnfsulfide may be added to thev metal oxide frit primer ltodeter degradation ofthe polymer. Examples of' suchmixtures are the combination of molybdenum trioxivde with cobaltous oxide fn't, molybdenum sulfide with cobaltous oxide frit, chromic oxide with cobaltous oxide frit and-molybdenum trioxide and chromic oxide with cobaltousV oxide fn't primer.

Themetal oxide frit employedin thisprocess is in a finely dividedstate or a powder which will pass through a i mesh screen and Which will preferably pass through a300V mesh` screen in the` U.S; Bureau of Standards 'Ihe particles are dispersed inl a volatile organic vehicle or dispersant before or during the time of blending` with thehalogen-containing polymer and the more finely divided the particle size of the frt, the better the dispersion. Suitable dispersants are the same as those recited above for thehalogen-containing polymer.

In preparing the compositions of this invention, be tween about 5 ,parts by weight and about 60 parts by weight, preferably between about 20 parts by Weight and about 50, parts by weight of the metal frit are blended with each l100 parts by weight of halogen-containing polymer, The polymer to metal oxide -frit ratios most preferably employed ,is 'between about 3:0.5 and about 3:2. Generally, where maximum chemicalgresistance is required,4 the metal oxide frit constitutes a minor proportion of the composition, whereas where maximum bond strength is required, ,the metalV oxide frit constitutes a proportion of the composition approaching 50 percent by weight or more.

The primer coating compositions of the present invention comprising a Volatile organic liquid metal oxide fritand halogen-containing polymer are used as coatings on various substrates. These coatings may be applied to metal surfaces, for example, st eel,`lnconel, Mouel, zinc, cadmium, magnesium, brass and aluminum surfaces, to asbestos surfaces, toV concrete surfaces, to glass surfaces and togany plastic surface which will withstand high temperatures, for example, temperatures upto about 600`` F. without degrading. Examples of such plastic surfaces -are-HaA polyurethan,r surface and a silicone plastic surface. The primer coatingcompositions.canbe laid down on the substrate s an initial coatwhieh.` adheres to the surface and to subsequent coatings of unblended polymer which form a surface coating on top of the initial coat. Examples of some of'the' applications for this type of coating, are coatings' for metal reactors and laminates bonded-to suitable fabrics such as glass cloth. The primer coating compositions of this invention, however, can also be applied to a substrate in a desired thickness and used as the sole surface coating. This application is illustrated by the use of chlorotriuoroethylene polymer blended with cobaltous oxide frit for use as a release coating on tire molds, etc. In cases Where the primer coating composition is the only coating applied to a substrate it is generally preferred to employ a peruorohalooleiin plastic in the primer composition. While the metal oxide frit when present in Vthe iinal coating decreases the chemical resistance of the coating, still the amount of peruorohaloolen plastic used may provide sujicient chemical resistance for the desired application. For some uses such as release coatings, very little chemical resistance may be required. Sometimes only a small amount of metal oxide frit Within the lower portion of the above range need be employed in the primer coating composition to give thedesired adherence. This is very often the case when applying a coating to a natural or synthetic fabric where the coating permeates the interstices of the Woven bers and is thus mechanically bonded to the fabric. small amount of metal oxide frit need be employed, that its eifect on the polymer in the primer coating composition is almost negligible. In cases where the coating material will be exposed to strong chemical action it is preferable to employ the primer coating composition as the initial coat over which a compatible chemically resistant plastic coating is applied. When maximum chemical resistance and bond strength is desired it is most preferred to employ a plastic peruorohaloolefin polymer which is the same polymer in the primer coating composition as in the subsequent unblended polymeric coatings applied to the substrate. Suitable for this purpose are the plastic polymers of chlorotriuoroethylene and tetrafluoroethylene.

Although dissimilar polymers may be employed if so desired they must be compatible and it is generally preferred that the halogen-containing polymer in the primer coating composition contains the same amount or less iluorination than the unblended polymeric coatings to be applied thereon. Such a construction is shown in the accompanying gure.

Previous primer coatings have required that a mixed coa be applied prior to the application of a nal coat. However, when using the blend of the present invention the final unblended coating can be applied directly over the primer coat. This development represents an important chemical and economic advantage over primers previously used. Additional advantages include the strong adhesion to the substrate and to the unblended plastic over-coat, the absence of delamination upon aging, the flexibility, high temperature stability and chemical resistance of these primers over most of those known and used heretofore.

To obtain a tine particle size of the metal oxide frit, the inorganic compound may be dry milled or milled in a volatile vehicle for a period of from 1 to 20 hours, more often for a period of from 2 to- 5 hours or until the desired particle size is obtained. The milled frit is then added to the halogen-containing polymer dispersion to provide a dispersion having a total solids concentration of between about 20 and about 80 percent total solids; preferably between about 30 and about 65 percent total solids. Another method of reducing the particle size of metal oxide frit comprises milling the frit after it `has been added to the halogen-containing polymer dispersion. In the case of chlorotriiluoroethylene polymer the milled frit can be added to any of the commercially available dispersions of that polymer which are disclosed in U.S. Patents Nos. 2,775,569 and 2,686,-

In this instance such a 767. Any suitable grinding apparatus may be employed `for this purpose, for example, a ball mill, a roller mill and a pebble mill.

In addition to the dispersion of the metal oxide frit and halogen-containing polymer, the primer compositions of this invention can contain various additives which are included to alter or improve some of the physical characteristics. For example, plasticizers can be added. Suitable plasticizers include the low molecular weight perfluorochloroolen polymers, such as the polymers of and telomers of chlorotriuoroethylene. The low molecular weight homopolymer of chlor-otrifluoroethylene ranges from relatively mobile liquids to waxes. One of the preferred low molecular weight telomers of chlorotriuoroethylene is the homotelomer which has the general formula in which n varies `from about 4 to about 20. l These plasticizers are soluble in the volatile dispersing vehicle and when used, they are added in an amount between about 1 and about 40 parts by weight per 100 parts by weight of the halogen-containing polymer. Although the addition of plasticizers is preferred since it results in more flexible coatings having smooth glossy surfaces, it is not an essential ingredient in the primer coating composition.

Chromic oxide may be added to increase bonding strength of the primer base coat to a metal surface and is used only when extremely high bonding strengths are required. Other bonding aids which can be added to the blend are potassium permanganate, molybdenum sulde and a polyurethan prepared by the reaction between a polyisocyanate and a polyalcohol. Examples of suitable polyurethans employed for this purpose are the reaction products of diphenylmethanediisocyanate and polyethyleneglycol, toluenediisocyanate and polyethyleneglycol, diphenylmethanediisocyanate and polypropyleneglycol, diphenylmethanediisocyanate and propyleneglycol, and diphenylmethanediisocyanate and propyleneglycol and monoricinoleate.

Additives which stabilize the halogen-containing polymers, particularly the periiuorohaloolen polymers against the effects of thermal degradation, can also be included in the primer composition of this invention. Such additives include barium peroxide, lead dioxide, chromic oxide, chromic suliide, cadmium oxide, zinc sulfide, molybdenum trioxide, molybdenum sulfide, stannic oxide'and stannic sulfide. When added, the stabilizer constitutes between about 0.1 and about 5 parts by weight per 100 parts by weight of polymer. -Inert llers such as, for example, mica or bentone can also be added to the primer composition in which case, they constitute from 0.1 to 20 parts by weight per parts by weight of polymer. The addition of these llers aids in the application of primer to a substrate by the method of dipping or slush coating, although the same effect can be accomplished by increasing the solids content in the dispersion, such as by increasing the amount of metal oxide frit and/lor polymer in the dispersion.

After the primer coating composition has been prepared and thoroughly mixed, it can be applied to a surface by using a spray, dip, knife or flow coating technique depending upon the 'viscosity of the dispersion, solution or slurry. After the primer composition has been applied to a substrate by any of the above techniques, it is fused. into a continuous adherent film by heating. Fusion temperatures range between about 350 F. and about 600 F., preferably between about 450 F. and about 56.0 F., for example, 500 F. to 520 1P., and are applied for a period of from about a few seconds to about 2 hours, preferably for a period not in excess of about 1 hour. 'In cases where the primer composition contains a plastic periluorohalioolen polymer and no plasticizer, the fusion is effected by heating the primer composition at a tem- Parature. abovethe iii-st order.A transition temperature. of the polymer which is 'about 220 C. in the. case of polyf chlorotriiluoroethylene. Generally, the higher the fusion temperature, the shorter the .residence period of the primer .coating composition at Vthat temperature. The residenceperiodgis also determinedby the method employed lfor heating. For example, thesub'strate may be placed in anoven and baked for a period of hours or it maybe lflame sprayed at a very high temperature (about 600 i thicknesses of not more than about 6 mils are employed,

since at higherthicknesses there isatendency for the Vcoating to mud crack.

In both ofthe above cases ,a minimum thickness of Y about 2 mils. of the primer coating composition is employed. lThe primer coating composition may be applied iu a seriesfof coating steps or it may be applied in a single step. When used as a base coat or intermediate coat, the outer and iinal coatings vof unblended polymer, i.e. polymer which contains no metal oxide frit, is applied in thicknesses ranging between about 5 and about 25 mils, and preferably between about 8 and about l2 mils.

Ina preferred embodiment two applicationsV of the primer coat, wherein each application amounts to about a 2 mil thickness, are, laid'down on va substrate and fused and about 10 mils of outer coating is applied thereon and cured.

After the nal coating of unblended plastic vis applied to the surface, the coating is cured thereon at a temperature between about 350 F. and about 600 F., preferably at a temperature between about 450 F. and about 550 F. depending upon the amount of plasticizer present for a period of from about 2 hours to about 25 hours, preferably for a period not exceeding l2 hours.

When fusing or curing the primer coating, the adhesion to a'surface may be enhanced 4by applying pressure to the coated surface. The application of pressures up to about 7,000 p.s.i.g. or higher are at times particularly useful when it is desirable to employ temperatures within the lower portions of the fusing and curing ranges set forth above. When preparing a laminate the use of pressure is preferred since 'the liquid primer coating, which is forced into the interstices of the fabric, provides a better bond with the fabric.

The finished coating, which is prepared by any of the methods or by the modification of any of the meth'ods set forth above, is strongly adherent to the subst-rate a-nd can not be peeled, chipped or cracked. The coated portion can be aged in the presence of strong acids or alkalies, at elevated temperatures with no noticeable weakening of theadherent strength. While I do not wish to be bound or limited by any particular theory of operation, it is believed that the metal of the metal oxide frit forms a coordination compound With a halogen of the polymer thus providing a chemical bond and that the metal of the metal oxide frit plates out lon the substrate, promo-tes the growth of nodules and provides dendrite growth on the surface ofthe metal. This theory would account for the exceptional adhesive properties of the primer.

The following `examples are offered as a better understanding of the present invention and are not to be construed vas unnecessarily limiting` thereto.

In `each of the following examples Where the prime-r coating compositions were used on steel panels, the steel was degreased and grit blasted before the primer was ap-.

plied. Detailed informationen thepreparation-ofthe. Y

primer coatingsI andthe application of the coatings is given in Examplesfl, Ltandv 5. `Similar techniques were u'sedin each of the examples reported in 'the table.

The following blend Wasprepared` Weight Grams Percent N on-Volatiles:

Hornopolymer of Ghlorotritluoroethylene (NST 310 C. 23.9 860 OQO Frit obtained from Harshaw chemical Company* 8. 1 288 Volatiles:

Ohlorotriiiuorethylene 10-200 Wax Plasticizer (2O percent non-volatile--l hours at 480 F.) 8` 0 290 ylene 36. 0 1, 297 Diisobutylketone. 24. 0 B65 Screen analysis of CoOtrlt purchased from the Harshaw Chemical Company Percent 325 mesh 58 42 200 mesh 19. 99 140 mesh mesl1 Q Pan 325 mesh) Y 21. 59

The above primer coat was prepared by mixing 2880 grams of polychlorotritluoroethylene dispersion (40 percent by weight of polychloron'iiiuoroethylene dispersed in a 50-50 mixture of xylene and diisobutyl ketone) with 288 grams of CoO frit (73.5 percent C00) in a pebble mill. After milling for 4 hours, 432 grams of xylene was added to readjust the solids t'o 40 percent.

Two coatings of the above prepared primer coat were applied to steelpanels by spraying. After partial air drying, each coat was baked for 45 minutes at 510v F. (substrate temperature). Six coats of commercial NW-ZS-'DR dispersion (a dispersion of polyohlorotriuoroethylene, NST 310"Y C.) `were applied over the primer coat by spraying. After partial air drying, each of the intermediate coats was `baked for 45 minutes at 500 F. (substrate temperature) and the'sixth coat was baked for live hours and'45 minutes at'500" iF. (substrate temperature) after which the panel Was quenched in water. The total primer thickness was 4 mils and the total thickness of polychlorotriuoroethylene was 10 mils as determined with a lm thickness gauge.

A panel Ythus coated Was subjected to steam, 240 F. and 10 p.s.i.g., for 100 hours Without loss of adhesion. Unprimed polychlorotriluoroethylene coatings lose adhesion to steel after onehour of similar steam treatment. Another panel thus coated was heat aged in an oven at 300 F. for 100 hours without loss of adhesion.

The above primer was ,prepared by mixing 3600 grams of polychlorotriuoroethylene dispersion (30 percent by Weight of polychlorotriilworoethylene Idispersed in amyl acetate) with 360 grams of CoO frit`(73.5 percent COO) in a pebbleumill for 4 hours. Aftermilling, 360'grams of amyl acetate was decantedto adjust `the solids to 40 percent.

A, portionof theabo,ve, dispersion was used to prepare a dip 'coating primer by decanting 202 grams of amyl acetate and adding 286 grams sof copolymer solution (12.2 percent by weight of copolymer in amyl acetate). This primer was thinned with amyl acetate to a Zahn G-2 cup viscosity of 30 seconds. Two coats of primer were then applied to a 0.25 inch steel rod by immersing the rod in the primer, withdrawing slowly and air drying and baking for 45 minutes at 510 F. (substrate temperature) between each coat. Four coats of commercial N-Z dispersion (a Vdispersion of polychlorotriuoroethylene and copolymer of chlorotriuoroethylene and vinylidene iluoride in amyl acetate) were then applied over the primer coating. The N-2 dispersion was thinned to a Zahn G-2 cup viscosity of 20 seconds and the rod was baked for 45 minutes at 500 F. (substrate temperature) after each immersion until the inal coat, which was baked for 5.5 hours at 500 F. (substrate temperature), was applied.

The total primer coat thickness was 2.5 mils and the thickness of the total unprimed dispersion was 4 mils as measured with a micrometer. The coated steel rod was subjected to steam, 240 F. and 10 p.s.i.g., for 100 hours Without loss of adhesion.

EXAMPLE 3 'Iwo six-inch long, one inch diameter glass reinforced epoxy tubes (constructed -of glass cloth and Epon 828 resin cured with metaphenylenediamine catalyst) were dip coated with the primer prepared in Example 2 `followed by N-2 dispersion also described in Example 2. The tubes received two coats of primer thinned to a Zahn G-2 cup viscosity of 30 seconds with amyl acetate. Each coat was baked 45 minutes at 510 F. (substrate temperature) before applying the next coat. Three coats of N-2 dispersion thinned to a Zahn G-Z viscosity of 20-26 seconds with amyl acetate were then applied over the primer by dip coating. The two intermediate coats of N-2 dispersion Were each baked for 45 minutes at 500 F. (substrate temperature) after applying and the iinal coat was baked for four hours at 500 F. (substrate temperature). Upon completion of the final bake, the tubes xwere quenched by immersion in water. It was impossible to strip the primed coating from the tubes.

Similar tubes were dip coated without primer by applying live coats of N-2 dispersion thinned to a Zahn G-2 cup viscosity of 26 seconds with amyl acetate to the tubes. The first two coatings were baked for 45 minutes at 510 F. (substrate temperature) after each application; coats 3 and 4 were baked for 45 minutes at 500 F. (substrate temperature) after each application and the final coat was baked for six hours at 500 F. Upon completion of the final bake, the tubes were quenched by immersion in Water. The unptimed coating could be stripped very easily from the tubes.

The above primer was prepared by mixing 3240 grams of polychlorotriuoroethylene dispersion (30 percent by Weight of polychlorotlluoroethylene dispersed in amyl acetate) and 486 grams of CoO frit (73.5 percent COO) in a pebble mill fo-r 4 hours. After milling, 8l grams of amyl acetate was decanted to adjust solids to 40 percent and 2679 grams of this primer was used to prepare a dip coating primer. Amyl acetate (186 grams) was decanted and copolymer solution, 286 grams (12.2 percent by weight of copolymer in amyl acetate) was added.

The dip coating primer was thinned with amyl' acetate to a Zahn G-2 cup viscosity of 32 seconds. Two coats of primer were applied to a 0.25 inch steel rod by immersing the rod in the primer, withdrawing slowly and air drying and baking for 45 minutes at 510 F. (substrate temperature) after each coat. Four coats of commercial N-Z dispersion were then applied over the primer with baking Ifor 45 minutes at 5 00 F. (substrate temperature) for each of the intermediate coats and baking for 5.5 hours at 500 F. (substrate temperature) for the final coat. The commercial N-2 dispersion used above for coating had been thinned to a Zahn G-Z cup viscosity of 20 seconds before it was applied by dip coating.

The total primer coating thickness was 3.0 mils and the total 4N--2 dispersion coating thickns was 3.0 mils as measured withV a micrometer. The coated steel rod was subjected to steam, 240 F. and 10 p.s.i.g, for 100 hours without loss of adhesion.

EXAMPLE 5 Weight Percent Grams A master batch of CoO frit was prepared by milling 2300 grams of CoO frit (73.5 percent CoO) and 1450 grams of volatile vehicle (50 percent xylene and 50 percent diisobutyl ketone) in a one gallon pebble mill for four hours. To a one gallon can was charged 475 grams ofthe C00 master batch prepared above and 2880 grams of commercial CNW-ZS-TR dispersion (a dispersion of polychlorotriuoroethylene in xylene and diisobutyl ketone). ing in a paint shaker for one hour.

T-wo coats of the above prepared primer were applied by spraying onto a steel panel with air drying and baking for 30 minutes at 540 F. (substrate temperature) between each application. Five coats of commercial NW-25-TR dispersion (40 percent by weight of polychlorotrifluoroethylene dispersed in xylene and diisobutyl ketone Zahn G-l cup viscosity 32 to 34 seconds) were applied over the primer coating Iby spraying. Each of the intermediate coats was air dried and then baked for 45 minutes `at 540 F. (substrate temperature) before applying the next coating. The iinal coat was baked for seven hours at 540 F. Upon completion of the final bake the steel panel was quenched by immersion in water. Four additional panels were similarly prepared.

One of the coated panels was subjected to steam, 240 F. and 10 p.s.i.g., for 100 hours without loss of adhesion. Other coated panels Were subjected to 37 percent hydrochloric acid, 98 percent sulfuric acid, 85 percent phosphoric acid and 50 percent sodium hydroxide for 504 hours at 180 F. without loss of adhesion.

While the above examples illustrate the economy and superiority of chemically resistant coatings while eliminating the necessity for a mixed coat, it should be noted that mixed coats can be used vif desired.

The following examples in Table I were carried out using an intermediate coat as a means for introducing stabilizers into the coating compositions which were applied and fused to steel panels. In each case a clean steel panel Was coated with primer containing polychlorotriuoroethylene (NST about 310 C.), cobaltous oxide The ingredients were mixed uniformly by shakplied and baked thereonbefore Table I Example Example Example Example 6 7 8 9 N-2 l Dispersion in Grams 100Y Y N W-25-TB. Dispersion,

Grams 100 200 200 200 Xylene, Grams Y 10 1215 v' 12. 5 1,2. 5 Mica, Grams- Y p, 3 3 n 3 3 C Irit, Grams 3 1.5 l. 5 1. 5 Mo0, Grams y 0. 5 C riOs,v Grams 0. 5 0.5 M082, Grams 0.5 Percent Solids 35,3 39 39 39 Temperature of Fusion, F 560 .A 560 560 560 Remarks (2) l (2) (2) (2) 130 percent by weight oi polyehlorotrluoroethylene; Brookfield viscosity about 10,000 centipolses.

2Good adhesion oi nlm.V -FilmY shows Ano evidence of degradation and has good ow properties.

Although lthe experiments of Examples 6, 7, 8 and 9 employ Vthe technique whereby the stabilizer is introduced in au intermediate coat, equally satisfactory results'can Y b e obtained by introducing the stabilizer directly into vhaving strong adhesion to substrates and a high degree of chemical resistance.

The invention herein described relates to a primer coating composition comprising a volatile liquid dispersion vehicle, a polymer of a halogen-containing olen, particularly a peruorohalogenated oleiin polymer and a metal oxide frit of a metal above the fourth group of the Periodic Table having a boiling point between 600"l C. and 1500 C. The resulting 'dispersion is fused and cured on a substrate to give a strongly adhesiveV and chemically resistant coating thereon. The method for preparing the primer coating compositions of this invention may be any of the methods Vor any of the Various modifications and alternatives of the procedure herein described and may become apparent to those skilled in the art without departing from the scope of this invention.

Having thus described my invention I claim:

l. A composition comprising arvolatile organic dispersing vehicle, a solid perfluorohaloolefin polymer se- 'lected from the group consisting of chlorotriiiuoroethylene homopolymer, chlorotrifluoroethylene vinylidene fluoride copolymer, and periluoropropcne vinylidene fluoride copolymer, and a cobaltous oxide frit, said cornposition containing between about 5 and about 60 parts by weight of cobaltous oxide frit per 100- parts by weight of perfluorohalooleiin polymer.

2. The composition ofclaim 1 wherein the Vnormally solid peruorohaloolen polymer'is a homopolymer of chlorotrifiuoroethylene. l

3. The composition of claim l wherein the normally "solid peruorohaloolen polymer is the copolymer of chiorotrifluoroethylene and vinylidene fluoride having between 20 and 69 mole percent of chlorotrifiuoroethylene.

4. The Acomposition vof claim lwherein the lnormally solid peruorohalooletin polymer is the copolymer of chlorotriiluoroethylene and vinylidene fluoride having above about 70. and below 10()k mole percentof `chlorotrifluoroethylene.

. A 12 Y Y Y 5. Thecomposition of claim l wherein theV normally solid perfluorohaloolen polymer is the copolymer of peruoropropene andA vinylidene fluoride.

V6. The composition of claim `l wherein the volatile organic vehicle-is amyl acetate.

7. The composition of claim 1 wherein the volatile jorganic vehicle is xylene. n

8. The composition of claim l wherein the volatile organic vehicle is a mixture of diisobutyl rketone and xylene.

9. A primercoating composition comprising a volatile organic dispersing vehicle, parts by weight of a solid pertluorohaloolefin polymer selected from the group consisting of Vchlorotriiuoroethylene homopolymer, chloro: triuoroethylene-vinylidene iiuoride copolymer and perf iluoropropene-vinylidene iiuoride copolymer between about 5 and about 60 parts by weight of a cobaltous oxide frit and between about 0.1 and about 5 parts by weight of a polymer stabilizer.

V10.7"i'he primer of-claim 9 wherein the stabilizer is molybdenum trioxide.

1l. The primer of claim 9 wherein the stabilizer is chromic oxide. l

12. The primer of claim 9 whereinthe stabilizer is molybdenum sulfide.

13. An article of manufacture which comprises a substrate and a coating thereon comprising 100 parts by weight of fused solid periluorohaloolen polymer selected from the group consisting of chlorotriuoroethylene homof polymer, chlorotrifiuoroethylene-viuylidene fluoride copolymer and perliuoropropene-vinylidene uoride copolymer, and between about 5 and about 60 parts by weight of a cobaltous oxide frit.

14. The article of claim i3 wherein the substrate is metal.

15. An article of manufacture which comprises a substrate, and an intermediate adhesive coating of between about 2 and about 6 mils thickness comprising 100 parts by weight of a fused solid perfluorohalooleiin polymer selected from the group consisting of chlorotrifluoroethylene homopolymer, chlorotriuoroethylene-vinylidene iiuoride copolymer, and periluoropropene-vinylidene uoride copolymer, and between about 5 and about 60 parts by weight of a Icabaltous oxide, and an outer protective coating comprising a normally solid polymer of a periluorohaloolefin.

16. An anticle of manufacture which comprises a metal substrate, an intermediate adhesive coating of between about 2 and 6 mils thickness comprising 100 parts by weight of a fused solid high molecular Weight homopolymer of chlorotriiluoroethylene, between about 1 and about 40 parts by weight of a low molecular Weight polymer of chlorotriuoroethylene, and between about 5 and about 60 parts by weight of a cobaltous oxide frit, and an outer protective coating comprising a polymer of chlorotriiluoro ethylene.

17. 'Ehe article of claim 16 wherein the cobaltous oxide frit is produced by fusing cobaltous oxide and an alkaline borosilicate glass.

18. A process which comprises 1) yapplying to a substrate a coating composition comprising a volatile organic dispersing vehicle, 100 parts by weight of a solid peruoroh haloolen polymer selected from the group consisting of chlortriuoroethylene homopolymer, chlorotriuoroethylene-vinylidene fluoride copolymer and pcruoropropene-vinylidene fluoride copolymer, and between about 5 and about 60 parts by weight of a cobaltous oxide, and (2) heating said coating composition to a temperature between about 350 F. and about 600 F. to provide a fused adherent coating on the surface of the substrate.

19. A process which comprises I(1) applying to a metal a coating composition comprising a volatile organic dispersing vehicle, 100 parts by weight of a solid peruorohalooleiin polymer selected from the group consisting of chlorotriiluoroethylene homopolymen chlorotriiluoroethylene-vinyli'clene uoride copolymer and pertluoroprofsene-vinyldene uoride copolymer, and between about 5 and about 60 parts by Weight of a cobaltous oxide, (2) heating said coating composition to a temperature between about 350 F. and about 600 F. to provide a fused adherent coating surface on the substrate, (3) applying thereona coating of a solid peruorohalooleiu polymer having a molecular weight above 50,000, and (4) curing the entire coating at a temperature between about 350 F. and about 600 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,388 Joyce Ian. 8, 1946 14 Dorst Jan. 24, 1950 Osdal July 24, 1951 Sanders Sept. 4, 1951 Ikeda Apr. 8, 1952 Robinson Nov. 25, 1952 Rubin May 12, 1953 Teeters Aug. 17, 1954 Dorst May 3, 1955 Finholt Mar. 6, 1956 Smith Apr. 23, 1957 Dipner May 20, 1958 Barnhart et a1. Feb. 17, 1959 Barnhart et a1 Feb. 17, 1959 

1. A COMPOSITION COMPRISING A VOLATILE ORGANIC DISPERSING VEHICLE, A SOLID PERFLUOROHALOOLEFIN POLYMER SELECTED FROM THE GROUP CONSISTING OF CHLOROTRIFLUOROETHYLENE HOMOPOLYMER, CHLOROTRIFLUOROETHYLENE - VINYLIDENE FLUORIDE COPOLYMER, AND PERFLUOROPROPENE - VINYLIDENE FLUORIDE COPOLYMER, AND A COBALTOUS OXIDE FRIT, SAID COMPOSITION CONTAINING BETWEEN ABOUT 5 AND ABOUT 60 PARTS BY WEIGHT OF COBALTOUS OXIDE FRIT PER 100 PARTS BY WEIGHT OF PERFLUOROHALOOLEFIN POLYMER. 